In synchronous data networks, a data clock is transmitted over the network from a source to all other instances in the network. An example for a synchronous network is a TDM network of the PDH hierarchy (TDM: time division multiplex; PDH: plesiochronous digital hierarchy). Further, it is known to transmit data via asynchronous networks, such as packet switched networks (PSNs). In particular, there is also the possibility to transmit synchronous data via asynchronously transmitted data packets, e.g., to transmit TDM data via a packet switched network. At transition points between TDM networks and PSM networks, inter-working functions (IWFs) are used to accomplish the conversion between the different network types. Generally, when transmitting synchronous data via asynchronously transmitted data packets, also a data clock of the synchronous data is propagated via the asynchronously transmitted data packets. This is typically accomplished by reconstructing the data clock from the asynchronously transmitted data packets.
One known approach of reconstructing the data clock is the adaptive method, in which the synchronous data are assembled into data packets and transmitted without transmitting additional time information via the asynchronous packet network. A receiver reconstructs the data clock by adaptation to an average reception data rate and controlling a phase-locked loop (PLL) to generate the reconstructed data clock.
Another known method of reconstructing a data clock is the differential method, in which timestamps are included into the transmitted data packets and are used for reconstructing the data clock in the receiver.
However, these known methods are sensitive to variations in the transit time of the data packets through the packet network, which also results in variations in the reconstructed data clock. These variations are also referred to as wander. Further, these known methods are sensitive to a loss of packets, which results in wander as well. For example, a loss of data packets may occur if the data packet has an excessively large transit time through the packet network, thereby arriving too late to be used at the receiving instance, if the data packet is found to be defective after reception, e.g., due to bit errors, and discarded at the receiving instance, or if the data packet is actually lost, i.e., never received from the packet network.